Semiconductor manufacturers are constantly striving to keep up with applications that require faster speeds for their microprocessors or microcircuits. For example, at clock speeds greater than three gigahertz, a microcircuit can be required to couple signals to billions of transistors. Further, microcircuits are continuing to be used over a variety of applications requiring faster speed including modeling and simulation, games, and internet video processing. It is anticipated that microcircuits having faster speeds will continue to be designed for a broad range of systems such as highly parallel supercomputers, back-end servers, desktop systems, and a number of embedded applications.
The industry has made tremendous strides in reducing the gate delays within individual devices of a semiconductor component or microcircuit. This improvement in device speed is generally limited by the conductors between the devices. The conductors can include heavily doped semiconductor materials or conductive metal strips and are commonly referred to as metallization. Generally, the microcircuit includes a plurality of alternating layers of conductors and insulators or dielectric layers. The velocity of propagation of a signal through the conductor is a function of conductor delay. The delay typically depends on a number of factors including the type of conductor material, operating frequency, length of the conductor, spacing between conductors and the permittivity of the dielectric layers adjacent to the conductor. In one example, the conductors of a synchronous digital circuit are required to carry the clock pulses to thousands of locations on the microcircuit at precisely the same time. As the clock speeds increase, the conductor delays can result in a loss in synchronization such that the microcircuit cannot function correctly. By changing the conductor material from aluminum to copper, manufacturers have been able to reduce the delay of signals through their microcircuits. Further, manufacturers have reduced the permittivity or dielectric constant of the dielectric layers, thereby reducing the capacitance between the conductor and the dielectric layer. For example, materials such as hydrogen silsesquioxane (HSQ), methyl silsesquioxane (MSQ), fluorinated glass, or NANOGLASS™ can aid in lowering the dielectric constant.
As clock speeds further increase, the signal or clock pulse is not completely contained on the conductor. Instead, a portion of the signal travels through the dielectric layer adjacent to the conductor. This exposes the clock pulse to an inhomogeneous media. The clock pulse generally includes a square wave shape and contains various frequency components. Hence, the clock pulse spreads out, smears or becomes dispersed in time, because the various frequency components travel at different speeds through the inhomogeneous media. As the requirements for speed further increase, any improvement in reducing delays by changing the conductor and dielectric layer materials are limited. Further gains in reducing the delay can include a combination of reducing the conductor's length and increasing the cross-sectional area of the conductor. The costs for changing the geometry of the conductor can include more processing steps and push the limits of the statistical capability of the process.
We describe a structure for coupling a signal through a microcircuit. In one example of such a structure, a transparent, conductive portion is used to couple an electromagnetic wave to various parts of the microcircuit. In another example of such a structure, an insulating layer is used to couple an electromagnetic wave to various parts of the microcircuit.